This application is based on Japanese Patent Application No. 2000-191132 filed Jun. 26, 2000, the contents of which are incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to a rubber product with a metallic structure and a method of producing the same. More particularly, the present invention is concerned with a rubber product with a metallic structure formed of an aluminum material, wherein a vulcanized rubber is bonded to the metallic structure, and a method suitable for producing such a rubber product.
2. Discussion of Related Art
A rubber product with a metallic structure has been widely used in various fields. In the rubber product, a vulcanized rubber having excellent properties in view of flexibility, resiliency, viscoelasticity, cushioning capability, etc., is bonded to the metallic structure. For instance, such a rubber product with the metallic structure is used in vehicles such as automotive vehicles, and in mechanical equipments, as a vibration damping rubber member interposed between two members in a vibration or shock transmitting system so as to exhibit vibration damping or cushioning characteristics.
The vibration damping rubber member as the rubber product with the metallic structure used on the automotive vehicles, in particular, is required to have a reduced weight in order to improve fuel economy and to achieve high performance of the automotive vehicles. To this end, the metallic structure is formed of an aluminum material in place of a conventionally used ferrous material.
By using the aluminum material, in place of the ferrous material, for the metallic structure of the rubber product, the rubber product tends to suffer from a local cell formed due to galvanic corrosion (contact corrosion). Described more specifically, where the vulcanized rubber of the rubber product is formed from a rubber composition in which a large amount of reinforcing filler such as a carbon black is included for maintaining the hardness of the vulcanized rubber at a level suitable for use as the vibration damping rubber, the vulcanized rubber has a relatively low degree of volume resistivity, and accordingly has a relatively high degree of electric conductivity. In this rubber product, the metallic structure of the aluminum material (hereinafter referred to simply as xe2x80x9cmetallic structurexe2x80x9d) is likely to be corroded by contact with the vulcanized rubber having high conductivity, due to a large difference of an electric potential between the highly conductive vulcanized rubber and the metallic structure.
To prevent corrosion of the metallic structure of aluminum, the metallic structure is subjected to a chemical conversion coating treatment such as a chromate treatment or a phosphate treatment, for improving corrosion resistance of the metallic structure. Such a chemical conversion coating treatment, however, is not sufficient for preventing the corrosion of the metallic structure, and it is required to provide more effective technique to improve the corrosion resistance of the metallic structure.
As an alternative technique to prevent the corrosion of the metallic structure of aluminum by contact with the vulcanized rubber, the amount of the carbon black which is included in the rubber composition for forming the vulcanized rubber and which increases the conductivity of the vulcanized rubber is reduced so as to increase the volume resistivity of the vulcanized rubber. The reduction of the carbon black content, however, gives rise to another problems such as deterioration of the physical properties such as the hardness and strength of the vulcanized rubber, and deterioration of moldability of the rubber composition for the vulcanized rubber. In view of this, it is difficult or undesirable to reduce the amount of the carbon black for decreasing the volume resistivity of the vulcanized rubber.
The present invention was made in view of the background art described above. It is a first object of this invention to provide a rubber product with a metallic structure which has a reduced weight and which exhibits a high degree of corrosion resistance by minimizing the amount of the carbon black included in the rubber composition for forming the vulcanized rubber which is bonded to the metallic structure, so as to increase the volume resistivity of the vulcanized rubber, while assuring required physical properties such as the hardness and strength of the vulcanized rubber.
It is a second object of the present invention to provide a method suitable for producing such a rubber product with a metallic structure.
The first object indicated above may be achieved according to a first aspect of the present invention, which provides a rubber product with a metallic structure formed of an aluminum material, wherein a vulcanized rubber is bonded to the metallic structure, wherein an improvement comprises: the vulcanized rubber being formed from a composition in which a natural rubber and an acrylic rubber are mixed in a proportion of 90/10-60/40 by weight; and the vulcanized rubber having an island-sea structure in which fine particles of the acrylic rubber having a size of 0.1-100 xcexcm are dispersed in a matrix phase of the natural rubber.
In the rubber product with the metallic structure constructed according to the above-indicated first aspect of the present invention, the metallic structure is formed of an aluminum material, and the vulcanized rubber bonded to the metallic structure has an island-sea structure wherein a predetermined amount of the acrylic rubber is dispersed in the form of fine particles in the matrix phase of the natural rubber. The present rubber product is primarily characterized by this island-sea structure which is formed as described above. The thus formed rubber product has a reduced weight owing to the metallic structure of aluminum, and the vulcanized rubber bonded to the metallic structure has increased hardness owing to the presence of the fine particles of acrylic rubber distributed in the vulcanized rubber structure. Accordingly, the amount of the carbon black included in the rubber composition for forming the vulcanized rubber can be advantageously reduced so as to increase the volume resistivity of the vulcanized rubber, for thereby effectively preventing the metallic structure from being corroded by contact with the vulcanized rubber.
In the rubber composition for forming the vulcanized rubber of the present invention, the natural rubber and the acrylic rubber are mixed in a proportion of 90/10-60/40 by weight. In the vulcanized rubber obtained by vulcanization of the thus prepared rubber composition, the vulcanized acrylic rubber is dispersed in the form of fine particles having a size of 0.1-100 xcexcm in the matrix phase of the vulcanized natural rubber. According to this structure, the vulcanized rubber bonded to the metallic structure has desirable physical properties such as high hardness and strength, and the rubber product with the metallic structure exhibits a high corrosion resistance.
In a preferred form of the above-described first aspect of this invention, the vulcanized rubber has a volume resistivity of not lower than 1xc3x97106 xcexa9cm, for further improved corrosion resistance of the metallic structure.
The present invention also provides a vibration damping rubber member for use on automotive vehicles, which vibration damping rubber member is constituted by the rubber product with the metallic structure constructed as described above. The vibration damping rubber member constituted by the rubber product according to the present invention has a high corrosion resistance and a reduced weight, and exhibits the physical properties required by the vibration damping rubber.
The second object indicated above may be achieved according to a second aspect of the present invention, which provides a method of producing a rubber product with a metallic structure formed of an aluminum material, wherein a vulcanized rubber is bonded to the metallic structure, the method comprising the steps of evenly mixing an unvulcanized natural rubber material, and an unvulcanized acrylic rubber material in a proportion of 90/10-60/40 by weight, together with a vulcanizing agent capable of vulcanizing only the unvulcanized acrylic rubber material, so that the unvulcanized acrylic rubber material is finely dispersed in the unvulcanized natural rubber material; vulcanizing the unvulcanized acrylic rubber material finely dispersed in the unvulcanized natural rubber material; and vulcanizing the unvulcanized natural rubber material after a vulcanizing agent capable of vulcanizing the unvulcanized natural rubber material has been added, for obtaining the vulcanized rubber which is bonded to the metallic structure, the vulcanized rubber having an island-sea structure wherein fine particles of a vulcanized acrylic rubber having a size of 0.1-100 xcexcm and obtained by vulcanization of the unvulcanized acrylic rubber material are dispersed in a matrix phase of a vulcanized natural rubber obtained by vulcanization of the unvulcanized natural rubber material.
The second object indicated above may also be achieved according to a third aspect of the present invention, which provides a method of producing a rubber product with a metallic structure formed of an aluminum material, wherein a vulcanized rubber is bonded to the metallic structure, the method comprising the steps of: preparing an unvulcanized rubber composition by evenly mixing together an unvulcanized natural rubber material and an unvulcanized acrylic rubber material in a proportion of 90/10-60/40 by weight, and adding a vulcanizing agent for vulcanizing the unvulcanized natural rubber material and a vulcanizing agent for vulcanizing the unvulcanized acrylic rubber material; and vulcanizing a thus obtained mixture for obtaining the vulcanized rubber which is bonded to the metallic structure, the vulcanized rubber having an island-sea structure wherein fine particles of a vulcanized acrylic rubber having a size of 0.1-100 xcexcm and obtained by vulcanization of the unvulcanized acrylic rubber material are dispersed in a matrix phase of a vulcanized natural rubber obtained by vulcanization of the unvulcanized natural rubber material.
According to these methods described above, the vulcanized rubber having the island-sea structure in which the fine particles of the vulcanized acrylic rubber are evenly dispersed in the matrix phase of the vulcanized natural rubber can be bonded to the metallic structure formed of the aluminum material. Therefore, these methods described above permit the produced rubber product with the metallic structure to have an improved corrosion resistance and a reduced weight.